Method of making circuitized substrate with signal wire shielding

ABSTRACT

A method of making a circuitized substrate in which at least one signal line used therein is shielded by a pair of opposingly positioned ground lines which in turn are electrically coupled to a ground plane located beneath the signal and ground lines and separated therefrom by a common interim dielectric layer. The substrate may form part of a larger structure such as a PCB, chip carrier or the like.

CROSS REFERENCE TO CO-PENDING APPLICATIONS

In Ser. No. 10/790,747, filed Mar. 3, 2004, there is defined acircuitized substrate in which at least one signal line used therein isshielded by a pair of oppositely positioned ground lines which in turnare electrically coupled to a ground plane located beneath the signaland ground lines and separated there-from by a common interim dielectriclayer. An electrical assembly including the circuitized substrate aspart thereof is also defined. The substrate may form part of a largerstructure such as a PCB, chip carrier or the like. The presentapplication is a divisional application of Ser. No. 10/790,747.

TECHNICAL FIELD

The invention relates to circuitized substrates and particularly to suchsubstrates which might be utilized as part of a larger circuitizedsubstrate such as a printed circuit (or wiring) board, semiconductorchip carrier, or the like, and particularly to such substrates (andlarger products) which are adapted for processing high speed signalsacross various planes thereof. More particularly, the invention relatesto such substrates and larger products designed to shield signal linestherein and/or thereon.

BACKGROUND OF THE INVENTION

The need for higher speed circuitries in circuitized substrates such asthose used in multilayered printed circuit boards (PCBs), chip carriers,etc. have arisen due to technological advances, in turn giving rise tothe need for higher speed digital signal transmissions. If not properlyimplemented, the reduction in the rise and fall time of high-frequencydigital signals propagating within the final product, e.g., a PCB, maylead to a compromise in signal integrity, for example cross-talk noiseand signal distortions due to impedance mismatch.

A signal path on a PCB or chip carrier at relatively low frequencies maybe represented electrically as a lumped network of series resistancesand shunt capacitances. However, as the frequency is increased, thisapproach of lumped circuit modeling breaks down, and signal paths mustbe regarded as transmission lines. The common transmission linestructures used, for example, in PCBs, are microstrip, embeddedmicrostrip, stripline and dual striplines. The microstrip configurationsimply refers to the case where the conductor is separated from areference plane, either ground or power, by a dielectric. The striplineconfiguration, on the other hand, has reference planes above and belowthe conductor. A typical multilayer PCB of more than two signal layersmay have both stripline and microstrip geometries.

The present invention as defined herein is directed at reducing andsubstantially eliminating cross-talk noise between signal lines locatedon conductive layers in a circuitized substrate such as one used in amultilayered PCB or chip carrier by providing effective shielding of thesignal line(s) in the substrate (and therefore in the PCB or carrier ifutilized therein). Crosstalk, as is known, is a category of noiseinduced primarily by the electromagnetic coupling between signal lines.In multilayered PCBs, especially those of relatively complexconstruction, crosstalk can occur by the electrical coupling betweenrelatively closely spaced signal traces (lines). Crosstalk decreasesnoise margins and degrades signal quality. This, of course, can be amajor limiting factor in communication systems performance. Crosstalkincreases with longer trace coupling distances, smaller separationbetween traces, shorter pulse rise and fall times, larger magnitudecurrents or voltages being switched.

Inductive and capacitive coupling are the two known types of signalcoupling that are the crosstalk determinant in a multilayered PCBcircuit plane. These two types of coupling decrease with increasingdistance between source and receiver. Most crosstalk can be attributedto adjacent wires. Because parallel and adjacent wires on a PCBconductive layer interact both capacitively and inductively, thedistance over which adjacent wires are parallel needs to be carefullycontrolled. To minimize crosstalk, some high frequency designsincorporate ground planes under each signal layer, which have proven tovirtually eliminate the crosstalk between these layers. Ideally, then,crosstalk between neighboring signals can be reduced by maximizingsignal-to-signal spacing and by minimizing signal-to-ground distances.These factors, plus a host of others, contain many interdependencies andare often at odds with one another. For example, high wiring density isrequired to minimize interconnect delays as well as size, cost andweight. However, as signal lines are placed closer together, theirmutual coupling increases, with a corresponding rise in crosstalklevels.

The design of PCBs, chip carriers and similar structures which includecircuitized substructures (e.g., those often referred to as “cores”) aspart thereof, therefore, has become quite a challenging task, especiallywhen designing high-performance and high-density final products. Mostsignificantly, electromagnetic coupling between the adjacent signallines (aka traces) is one factor that sets the upper limit to theinterconnect density.

In one known multilayered PCB structure, the structure includes a firstlayer having an electrically conductive plane for electrical connectionto a common armature contact of a relay, the electrically conductiveplane being sized to substantially cover a mounting footprint of therelay. This PCB structure also includes a second layer parallel to andelectrically separate from the first layer, the second layer having anelectrically conducting first section for electrical connection to anormally-open contact of the relay and an electrically conducting secondsection for electrical connection to a normally-closed contact of therelay. The first and said second sections are electrically separate fromeach other and, in combination with each other, are planar and sized tosubstantially cover the mounting footprint of the relay.

In U.S. Pat. No. 6,529,229, first and second clock signal lines arepreferably mutually adjacent, and preferably weave around electrode padsand/or wiring patterns used to interconnect the driver ICs. Thepreferred even-odd variation of the interconnections between the driverintegrated circuits (ICs) and the clock signal lines facilitates themutually adjacent weaving layout of the clock signal lines, whichimproves their noise immunity. The clock signal lines preferably includein-line electrode pads to which the clock input terminals of the driverICs are coupled. The in-line electrode pads reduce reflection of theclock signals because they avoid characteristic-impedancediscontinuities.

Coupling semiconductor devices (integrated circuits or chips), includingthose of the multi-mode variety (analog and digital) onto PCBs, hasresulted in various attempts to reduce noise generation and theassociated problems. One attempt to solve the noise problem involves theaddition of decoupling capacitors placed near the active devices. Thedecoupling capacitors stabilize the current flowing to these devices.However, while the capacitor absorbs some of the voltage, an undesirablespike still occurs.

Another known attempt to manage switching noise in multi- or mixed-modestructures involve partitioning analog and digital functions. Thisprocess requires unique manufacturing processes and custom designs. Forexample, U.S. Pat. No. 6,020,614 suggests that noise can be reduced byestablishing boundary zones between the analog and digital circuits of asemiconductor substrate with the analog circuit having a separate powersupply bus from the digital circuit. Further, this patent mentionsproviding interconnect signal lines such that the isolated wires betweenthe circuits may functionally interact with other circuits while thesubstrate noise coupling from other circuits remains low. However,spacing the analog components from the digital components can wasteprecious semiconductor space, which is an important consideration inintegrated circuit (and PCB) design.

Another attempt to resolve switching noise problems in a multi-modestructure is addressed in U.S. Pat. No. 5,649,160. This patent suggeststhat the noise can be reduced by shaping the noise from the digitalcircuit and concentrating it in a single or a small number of parts ofthe frequency spectrum. This solution relies on the concept that thepresence of noise in the analog circuit is less important at certainfrequencies, and therefore the spectral peak or peaks from the digitalcircuit can be carefully placed to result in little or no interference.

Other approaches for arranging transmission lines on microwave circuitstructures are described in U.S. Pat. Nos. 6,429,752, 6,429,757 and6,522,214. And, in U.S. Pat. No. 5,031,073, there is described a PCB inwhich the board's circuitry is partitioned into a plurality of circuitregions which are selectively isolated with respect to input and outputsignals. Signal lines in one region are arranged in a closely spacedarray aligned with, but spaced from, a corresponding array in anadjacent region. Other shielding structures are described in U.S. Pat.Nos. 5,196,230, 5,684,340 and 6,040,524.

Additional examples of various PCB multilayered structures are shown anddescribed in more recent documents, these being U.S. Published PatentApplications US2002/0108780 A1, US 2002/0148637 A1, US 2002/0100613 A1and US2004/0009666 A1, the teachings of which are incorporated herein byreference, as are the teachings of the other documents cited in thisBackground.

As defined hereinbelow, the present invention defines a new and uniquecircuitized substrate in which cross-talk is substantially eliminatedbetween adjacent signal lines or between signal lines and adjacent linesdesigned to conduct power signals on a singular plane within thesubstrate. Such a substrate design, as taught herein, is of simplerconstruction and operates more expeditiously than many of thosedescribed above, is relatively less expensive to manufacture than same,and thus represents a significant advancement in the art. Of equalsignificance, the substrate defined herein is readily adaptable forutilization within larger circuitized structures such as multilayered,complex PCBs, chip carriers and the like.

DISCLOSURE OF THE INVENTION

It is a primary object of the present invention to enhance thecircuitized substrate art.

It is another object of the invention to provide a circuitized substratewhich is capable of operating effectively with a minimum of crosstalkwhile still allowing high density wiring patterns, if desired, e.g., tocouple electronic packages such as chip carriers thereto if incorporatedwithin a larger structure such as the aforementioned PCBs, chipcarriers, etc.

It is another object of the invention to provide a circuitized substratewhich can be manufactured and incorporated within larger structuresusing present technology and at less costs compared to present methodsused to manufacture such structures.

According to one aspect of the invention, there is provided a substratecomprising at least one dielectric layer having first and secondopposing sides, a conductive ground plane located on said first opposingside of said dielectric layer, at least one conductive signal linelocated on said second opposing side of said dielectric layer, and firstand second conductive ground lines located on the second opposing sideof the dielectric layer on opposite sides of the at least one conductivesignal line and electrically coupled to said ground plane located onsaid first opposing side of the dielectric layer. The first and secondconductive ground lines provide shielding for the at least oneconductive signal line during the passage of electrical current throughthe signal line.

According to another aspect of the invention, there is provided anelectrical assembly comprising an electrical component and a circuitizedsubstrate including at least one dielectric layer having first andsecond opposing sides, a conductive ground plane located on the firstopposing side of the conductive ground plane, at least one conductivesignal line located on the second opposing side of the dielectric layer,and first and second conductive ground lines located on the secondopposing side of the dielectric layer on opposite sides of the at leastone conductive signal line and electrically coupled to said ground planelocated on said first opposing side of said dielectric layer. The firstand second conductive ground lines provide shielding for the at leastone conductive signal line during the passage of electrical currentthrough the signal line. The electrical component is electricallycoupled to the circuitized substrate.

According to yet another aspect of the invention, there is provided amethod of making a circuitized substrate, the method comprisingproviding at least one dielectric layer having first and second opposingsides, positioning a conductive ground plane on the first opposing sideof the conductive ground plane, positioning at least one conductivesignal line on the second opposing side of said dielectric layer, andpositioning first and second conductive ground lines on the secondopposing side of the dielectric layer on opposite sides of the at leastone conductive signal line. The method further comprises the step ofelectrically coupling the first and second conductive ground lines tothe conductive ground plane located on the first opposing side of thedielectric layer such that the first and second conductive ground lineswill provide shielding for the at least one conductive signal lineduring the passage of electrical current through said signal line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, sectional perspective view of a circuitizedsubstrate according to one embodiment of the invention, showing thepositioning relationship of the opposed conductive ground lines and theinternal conductive signal relative to the conductive ground plane,according to one aspect of the invention;

FIG. 2 is an elevational view, in section, of the substrate of FIG. 1,showing the addition of other layers, and at least one component (twoare shown) for use therewith, so as to form an electrical assemblyaccording to one aspect of the invention;

FIG. 3 is an elevational view, in section and on a larger scale over theviews of FIGS. 1 and 2, showing a circuitized substrate according toanother embodiment of the invention; and

FIG. 4 is an elevational view, in section and on a larger scale over theviews of FIGS. 1 and 2, showing a circuitized structure according to yetanother embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims in connection withthe above-described drawings. It is understood that like numerals willbe used to indicate like elements from FIG. to FIG.

In FIG. 1, there is shown a circuitized substrate 10 according to oneaspect of the invention. As will be understood from the followingdescription, the resulting structure, in the broadest aspects thereofand as defined herein, is a circuitized substrate which includes atleast one electrically conductive signal line 13 which receiveselectrical shielding protection from two adjacent and opposedelectrically conductive ground lines 15 and 17, located on the samesurface of the board and thus in a planar relationship. As to beunderstood from the teachings herein, the circuitized substrate of theinvention is readily adaptable for use within (to thus form part of) alarger structure such as a multilayered PCB, chip carrier, or the like.Although only one signal line is shown, it is understood that severalsignal lines may be utilized, especially if the substrate is so utilizedwithin a PCB, chip carrier or the like, so the teachings of thisinvention are also applicable to utilization of such added lines and theprotection thereof. In one example wherein the circuitized substrate astaught herein is utilized in a multilayered, relatively complex PCB,several thousand signal lines may be utilized in combination with asimilar number of paired opposing conductive ground lines adjacentthereto. The invention is thus not limited to a singular signal and onepair of ground lines configuration.

The structure as shown in FIG. 1 may also form what may be referred toas a two signal and one power (2S1P) core structure, several of whichare presently made by the Assignee of the present invention and whichare then utilized as part of multilayered PCBs of complex constriction,also produced and sold by the present Assignee. If so utilized, oneexample of additional signal, ground and/or power layers which may beadded to form this larger PCB structure are shown in FIG. 2, describedherein below.

The structure shown in FIG. 1 comprises at least one dielectric layer 19on one surface of which are located the co-planar lines 13, 15 and 17.On the opposing surface is located a conductive ground plane 21 which,as shown, is substantially solid in configuration and extends across thelower surface substantially beneath the parallel lines 13, 15 and 17running thereabove. Lines 13, 15 and 17, and ground plane 21 are eachpreferably comprised of copper, and formed using conventional PCBmanufacturing processing, e.g., layer lamination of the solid sheetcopper foil for the ground plane and photolithographic processing forthe individual conductive lines. Further description is thus notbelieved necessary. In one example, the lines are from about 0.0005 toabout 0.002 inch thick, and are spaced apart a total distance of onlyabout 0.002 to 0.010 inch from one another. The interim dielectric layer(as well as other dielectric layers if used with the invention) ispreferably comprised of conventional material (e.g.,fiberglass-reinforced polymer resin, also known as “FR4” in theindustry. Other dielectric materials may include Teflon (a trademark ofE.I. DuPont deNemours and Company) and Driclad (a trademark of theAssignee of the invention). In one example, layer 19 may possess athickness following lamination of about 0.0015 to 0.015 inch. Once theopposed lines and ground plane are formed on the opposite sides of theinterim dielectric layer, this “subcomposite” is then bonded to a seconddielectric layer 23 and a second conductive layer (of signal and/orground lines) is formed, again using conventional techniques asdescribed above. The bonding of the second dielectric layer 23 ispreferably accomplished using conventional lamination processes whichutilize heat and pressure as part thereof. In one example of theinvention, temperatures from about 175 degrees Celsius to about 250degrees Celsius and pressures from about 100 pounds per square inch toabout 1,100 pounds per square inch are possible. Similarly, ifadditional signal, ground and/or power layers are desired (the preferredembodiment), these may be simply arranged in a stacked orientation andsimultaneously laminated with the layers in FIG. 1. Further descriptionis not considered necessary.

In FIG. 1, at least three conductive thru-holes 25, 27 and 29 are formedto provide electrical connections to additional circuitry, or, in thecase of ground lines 15 and 17, to the planar conductive ground plane21. The formation of such thru-holes is first accomplished by providingopenings within the structure, such as by using mechanical or laserdrilling, the later preferred for the instant invention. In one example,each thru-hole may possess an internal diameter of only about 0.003inch, following which a layer of copper 31, having a thickness of onlyabout 0.0005 inch, is plated thereon to provide the conductive medium.Significantly, the internally positioned signal line 13 does not coupleto the ground plane but instead preferably is coupled using thru-hole 25to another signal line 13′ (shown in phantom) on the underside of layer23. Similarly, the outer ground lines 15 and 17 may be coupled to yetanother ground line or plane such as represented by the numerals 33 and35, respectively. Such couplings using thru-holes is facilitated by theformation of conductive lands 37 on the illustrated dielectric surfaces,such land formation known in the art and further description is notdeemed necessary. Each land will in turn be comprised of copper and ofthe same thickness as the connecting line coupled thereto.

The structure shown in FIG. 1 in its simplest form may comprise thesingular dielectric layer 19 and opposing conductive lines 13, 15 and17, and plane 21. In the preferred embodiment, of course, more layersare needed to satisfy the more stringent functional capabilitiesdemanded of many of today's more complex PCB and other conductivestructures in which the invention will be utilized. By way of example,in FIG. 2, circuitized substrate 10 further includes third and fourthdielectric layers 41 and 43 (in phantom) bonded on opposite sides of thesubstrate, each of these dielectric layers including a conductive layerthereon (also in phantom). The first of these layers, represented by thenumeral 45, includes a plurality of conductive pads 47, each of which isdesigned for having an external conductor such as 49 secured thereto. Inone example, pads 47 are comprised of copper and the external conductors49 are preferably solder balls, e.g., those containing 63:37 tin:lead“eutectic” solder alloy. Alternatively, the solder balls may becomprised of another solder such as 90:10 tin:lead alloy. A total ofabout 3600 pads (and solder balls) may be used in one example of theinvention (another example of the high density construction theinvention is able to attain), and serve to electrically couple theresulting structure shown in FIG. 2 (now what can be referred to as aPCB or chip carrier or the like) to an external electrical component 51,a preferred example being a chip carrier known as a HyperBGA chipcarrier also produced and sold by the Assignee of the invention.HyperBGA is a trademark of the Assignee, Endicott InterconnectTechnologies, Inc. If component 51 is a chip carrier, then themultilayered structure including substrate 10 is preferably a PCB. Inanother example, component 51 may comprise a semiconductor chip which isdesigned for being directly coupled (surface mounted) onto the upperpads on the FIG. 2 structure. If a chip is being coupled, the FIG. 2structure is preferably a chip carrier, and, if so, smaller solder ballsare preferably used for this coupling purpose compared to those use tocouple a traditionally larger chip carrier coupled to a PCB. In additionto pads 47, the conductive layer 45 may also include additional signallines or the like thereon, e.g., coupling selected ones of the pads ifmandated by the electrical circuitry design of the final product usingthe invention.

In FIG. 2, there is also shown yet another conductive layer 53 on theunderside of the FIG. 2 structure (and also shown in phantom). Layer 53may comprise a plurality of conductor pads 55 (and other conductivecircuitry as shown) for coupling the structure to another electricalcomponent, in this case, preferably a PCB 57 (in phantom). In thismanner, the structure shown is preferably a chip carrier, and solderballs 59, preferably of one of the above compositions for solder balls49, are utilized to complete the connections. In one example, a total ofthe aforementioned approximately 3600 pads (and solder balls) are usedfor this connection to the above structure. Pads 61 are used to connectthe solder balls to the corresponding pads 55. Pads 55 and 61 are alsopreferably of copper, as are any other conductive lines or pads on thelayer 53 or on the upper surface of structure 57. This structure, asmentioned above, may also include additional internal conductive planesand/or lines (not shown) to provide greater functional capability forthe final structure. This structure is thus an electrical assemblyincluding the circuitized substrate defined above (with additionallayers to form a chip carrier) and chip 51 and PCB 57.

Such a chip carrier (or electronic package, as these are also referredto in the industry), or a semiconductor chip if utilized instead, wouldbe positioned in the approximate location illustrated in a substantiallyrectangular pattern of pads and corresponding solder balls. A similar,perhaps larger rectangular pattern is used on the PCB 57, as indicatedin FIG. 2 by the relative differences in size. This is not limitative ofthe invention however, as other patterns and sizes are possible.

In a particularly preferred embodiment of the invention as produced bythe Assignee of the invention, the circuitized substrate 10 of FIG. 1forms what is referred to as a “core” structure, which is then combinedwith other similar core structures (and other layers such as interimdielectric material sheets positioned therebetween prior to finalbonding) to form a multilayered PCB. In one example, five such “cores”are stacked atop one another, along with intermediate (interim)dielectric and conductive ground planes, to form a much larger PCBassembly. In one preferred example of such a final PCB structure, thestacked (and laminated) final structure is comprised of a first opposing(top) external conductive layer, dielectric layer, conductive groundplane, dielectric layer, a circuitized substrate “core” 10, dielectriclayer, conductive ground plane, dielectric layer, a second circuitizedsubstrate “core” 10, and continuing in a similar sequential order to afifth circuitized substrate “core” 10, followed by a dielectric layer,conductive ground plane, dielectric layer and, finally, a secondopposing (bottom) external conductive layer. The top and bottom externalconductive layers, conductive ground planes and the five “cores” 10 areelectrically interconnected, where desired, using conventionally drilledand plated through hole technology known in the PCB art. Thus, in thisparticularly preferred embodiment of the invention, very high density,shielded wiring can be achieved due to the multiple core layers andsmall geometry of the shielding structures that are possible on theinitial core structures utilized in the final product. This finalproduct is then capable of being successfully utilized in an electricalassembly such as a personal computer, mainframe, server, or the like,what may also be referred to generally as an “information handlingsystem.” As such, the structure will of course include additionalcomponents such as chips, resistors, capacitor, etc. as part thereof andwill be electrically coupled into the ultimate assembly's circuitry.

The embodiment of FIG. 1, in its simplest construction, thus representsa shielding structure for single-ended controlled impedance conductivelines (e.g. signal lines 13 between ground lines 15 and 17). A similarconfiguration can be achieved for differentially controlled lines byplacing the differential paired signal lines 13′ and 13″ between theground lines 15′ and 17′ (e.g. ground-signal-signal-ground) as shown inFIG. 3, the circuitized substrate 10′ of FIG. 3 thus described as anembedded differential pair coplanar circuitized substrate. Three groundplanes 21′, 21″ and 21′″, of substantially solid and planarconstruction, are positioned as shown in FIG. 3, as are adjacentconductive thru-holes 27′ and 29′ (which are electrically coupled tointerim ground plane 21′ as these were in FIG. 1. Thus, each pair ofadjacent and coplanar signal lines 13′ and 13″ form a differential pairwith reference (ground) planes 21′ and 21″ and the upper coplanaradjacent ground lines 15′ and 17′ providing the shielding for the upperpair 13′ and 13″, while ground planes 21′ and 21′″ and the loweradjacent and coplanar ground lines 15′ and 17′ form shielding for thelower pair of signal lines 13′ and 13″.

The embodiment of FIG. 4, circuitized substrate 10″, is similar inconstruction to that of FIG. 3 except for the addition of shieldingground lines 157 and 157′ on the same plane and between each respectiveupper and lower pair of signal lines 13′ and 13″. As understood, allground planes and ground lines shown in the drawings are electricallycoupled (to ground). In FIG. 4, one ground line is positioned betweeneach signal line, on both the upper and lower planes along which thesignal lines are located. Thus, in FIG. 4, signal lines 13′ and 13″ onone plane (i.e., the upper) are referenced to ground planes on oppositesides of this pair of lines (as in FIG. 3), while those of the othersignal lines are referenced to the ground planes opposite said pair. Akey feature of this construction of this embodiment of the invention isthat the signal line to signal line pitch (spacing) is approximately onehalf that of unshielded signal lines having the same impedance anddielectric thickness. Thus, a 2× improvement in wiring density can beachieved, allowing for a much higher density printed circuit board inthe same overall thickness. The structures depicted in FIGS. 3 and 4, ifincorporated within larger multilayered structures such as multilayeredPCBs, can also be referred to as an embedded differential pair coplanarwaveguide (FIG. 3) or a single-ended coplanar waveguide (FIG. 4)embedded within said multilayered structure, if this is the purpose ofsuch a PCB (to serve as a waveguide component).

There has thus been shown and described a circuitized substrateconstruction which significantly reduces cross-talk noise for aconductive signal line (or pair of lines) in which a separate conductiveground plane (or more, as defined) is used in combination with twoadjacent ground lines on the same plane as the signal line to provideshielding for the signal line, the ground plane located on a separateplane beneath all three lines and parallel thereto. The resultingstructure substantially reduces cross-talk noise between adjacent signallines and planes to result in a final structure capable of operating atboth high and low frequencies, the former especially desirable intoday's more complex board technologies. The signal patterns andresulting connecting structures as described herein are possible on ahigh density basis wherein the adjacent signal lines on one plane may beas closely spaced as only about 0.006 inch apart on the same plane. Thisrepresents a significant advancement in the art, particularlyconsidering that the structure as produced herein may be manufacturedusing conventional PCB technologies, thus representing a substantiallyreduced cost product to the end purchaser.

While there have been shown and described what are at present thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

1. A method of making a circuitized substrate, said method comprising:providing at least one dielectric layer having first and second opposingsides; positioning a conductive ground plane on said first opposing sideof said conductive ground plane; positioning at least one conductivesignal line on said second opposing side of said dielectric layer;positioning first and second conductive ground lines on said secondopposing side of said dielectric layer on opposite sides of said atleast one conductive signal line; and electrically coupling said firstand second conductive ground lines to said conductive ground planelocated on said first opposing side of said dielectric layer such thatsaid first and second conductive ground lines will provide shielding forsaid at least one conductive signal line during the passage ofelectrical current through said signal line.
 2. The method of claim 1wherein said first and second conductive ground lines and said at leastone conductive signal line are positioned on said dielectric layer usinga photolithographic process.
 3. The method of claim 1 further includingproviding first, second and third conductive thru-holes within said atleast one dielectric layer, said first and third conductive throughholes electrically coupling said first and second conductive groundlines to said conductive ground plane.
 4. The method of claim 3 furtherincluding providing a second dielectric layer on said conductive groundplane opposite said first dielectric layer and providing a secondconductive signal line on said second dielectric layer opposite saidconductive ground plane, said second conductive thru-hole electricallycoupling said at least one conductive signal line to said secondconductive signal line.